Heart disease is very serious and often requires emergency operations to save lives. A main cause of heart disease is the accumulation of plaque inside the blood vessels, which eventually occludes the blood vessels. Common treatment options available to open up the occluded vessel include balloon angioplasty, rotational atherectomy, and intravascular stents. Traditionally, surgeons have relied on X-ray fluoroscopic images that are planar images showing the external shape of the silhouette of the lumen of blood vessels to guide treatment. Unfortunately, with X-ray fluoroscopic images, there is a great deal of uncertainty about the exact extent and orientation of the stenosis responsible for the occlusion, making it difficult to find the exact location of the stenosis. In addition, though it is known that restenosis can occur at the same place, it is difficult to check the condition inside the vessels after surgery with X-ray.
A currently accepted technique for assessing the severity of a stenosis in a blood vessel, including ischemia causing lesions, is fractional flow reserve (FFR). FFR is a calculation of the ratio of a distal pressure measurement (taken on the distal side of the stenosis) relative to a proximal pressure measurement (taken on the proximal side of the stenosis). FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment.
Intravascular catheters and guide wires are utilized to measure the pressure within the blood vessel. To date, guidewires containing pressure sensors have suffered from reduced handling characteristics compared to standard guidewires that do not contain such components. Further, pressure-sensing guide wires have also suffered from reduced precision and accuracy characteristics with respect to making intravascular pressure measurements when compared to larger pressure-sensing devices, such as aortic pressure-sensing catheters. In particular, to date pressure-sensing guide wires have suffered from drift. Drift causes the pressure reading provided by the pressure-sensing guide wire to change (i.e., increase or decrease) over time as a result of factors associated with the device itself unrelated to the actual pressure within the vessel. As a result, in order to ensure proper FFR calculations, pressure-sensing guide wire must be repeatedly normalized (i.e., relative to an aortic pressure measurement made by a pressure-sensing catheter) during a procedure. This can increase the amount of time necessary to perform the procedure, require administration of additional pharmaceuticals (e.g., adenosine) to the patient, or both, which increases the chances for unwanted complications during the procedure.
Accordingly, there remains a need for improved intravascular devices, systems, and methods that include one or more pressure sensing components with no or minimal drift within a guide wire.